There are 2 types of graphics and it is very important to understand the difference between them.

Bitmap Images:
The first type are called Bitmaps (or raster images) and are based on pixels. One of the disadvantages of this type of graphic is that it does not scale well. If you resize a bitmap image, you may notice that the image quality suffers. To understand why this happens, you need to realize what it means for an image to be composed of pixels. If you open a bitmap graphic in an application such as Photoshop and begin to zoom in on the image, you will probably notice that the image is broken down into smaller squares at around 300-400%. Keep zooming in and this will become more apparent. Each of these little blocks is a pixel and can contain only 1 color. Because a pixel takes up a visible amount of space and can only be filled with 1 color, you can imagine that some special process must be in effect to create the illusion of smooth transitions between colors. This is a dithering technique called Antialiasing that attempts to give the illusion of smooth blends between colors as well as to diminish the jagged effects of curves and diagonal lines. In the graphic below, the bitmap is antialiased. If it wasn't, it would look even more jagged.

When scanning graphics into applications that deal with bitmap data only, make sure that you scan the image in at the exact size that you need. This will prevent you from having to resize the image and compromise the quality.

Bitmap

Vector

Vector Images:
The other type of graphic is called a vector graphic. Vector graphics do not use pixels and are based on mathematical formulas that represent curves and lines. Vector graphics are very smooth looking and can easily be resized without loss of image quality. This is not a math tutorial so we will try not to go too in depth, however, the following example may clear up what makes vector graphics so sharp and scalable.

Let's say that we draw a line that is represented by the equation 3x+2y-13=0. In order to double the size of that line, we would multiply the equation by 2 as follows 2(3x+2y-13=0). This should create a line that is 2x the size of the original and is based entirely on math and doesn't use pixels which means that there is no need for the application to use a dithering effect to give the appearance that the line is perfectly smooth... It already is.

So what if you need to bring a vector based image into an application that does not support them? If the graphics application you are using cannot handle vector files then save them as EPS (Encapsulated PostScript) files. An EPS essentially places a PostScript wrapper around your image and preserves all of the image data. In the case of a vector image, the mathematical equations that represent your vector image will remain and not be converted when brought into the application.